build!: raise the compile baseline to Java 21 and restore the reverted language features

[eschizoid]

Closes #217. Raises the compile baseline from Java 17 to Java 21 (LTS) across all modules — toolchain stays at 25 — and restores every language feature the Java 17 downgrade (#80) stripped, except unnamed _ (JEP 456 needs 22+; deliberately out of scope at an LTS floor).

What's restored

• Pattern-match switch over the sealed hierarchies in Either, Validated, EitherK, ValidatedK, DeepMap (the fieldIsoOf dispatch and extractDefaultStrategy; the sequential applyForward/applyBackward routing passes intentionally stay as chains), ValidatedOrderController — the "unreachable" fallthrough throws are deleted (exhaustiveness is compiler-checked now).
• Record patterns in Validated.combine, ValidatedK.map2, DeepMap.
• Sequenced Collections — getFirst() across codegen processors, demos, tests. Positional get(0)/get(1) pairs (Map key/value type args) intentionally stay indexed.
• try-with-resources on ExecutorService in BoundedAsyncTest + the Telescope javadoc example.
• Telescope.BridgeTelescope back to private — Java 21 accepts a private permitted subclass in the same compilation unit, so build: cross-compile to Java 17 (--release 17) #80's accessibility workaround goes away.
• options.release = 21 in all 14 module build files, @SupportedSourceVersion(RELEASE_21) on the 5 processors, README JVM badge → 21+.

Correction vs the issue text

#217 listed "restore BridgeProcessor switch emission" — that item is moot: the sealed-bridge dispatch emission was independently rewritten (after #80) to the lattice-routed Match.of(…).when(…).exhaustive() runtime builder, which is source-level-agnostic. Generated navigators/bridges therefore do not impose a -source 21 requirement on consumers; the only consumer-facing constraint is the runtime floor below.

Breaking change (release-notes callout)

• Consumers on Java 17–20 can no longer run telescope — artifacts are compiled at --release 21 (class-file 65), so the runtime floor is Java 21.

Deliberate behavior change (found in review)

Validated.combineAll now throws NullPointerException on a null list element where the old instanceof chain silently dropped it (producing a Valid with a shorter list — silent corruption). Loud failure over silent element loss; no caller or test relied on the old behavior.

This should ride the next minor-at-least version bump with the baseline called out in the release notes.

Test

Full ./gradlew spotlessApply build green across all 14 modules.

Note on codecov/patch

The exhaustive fieldIsoOf switch carries eight explicitly-dead throwing arms (documented in-source as DEAD-BRANCH-DEFENSIVE, "NOT coverage targets"): they exist so a future Mapping permit forces a compile error instead of silently mis-routing. codecov/patch counts those never-executed lines against the patch — that red is the deliberate price of compile-checked exhaustiveness, not a coverage gap; every reachable branch is pinned by a named test (see the review-fleet coverage report).

[codecov]

Codecov Report

❌ Patch coverage is 72.13115% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.60%. Comparing base (6f789fc) to head (2523712).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...in/java/io/github/eschizoid/telescope/DeepMap.java	44.44%	9 Missing and 1 partial ⚠️
...b/eschizoid/telescope/codegen/BridgeProcessor.java	72.72%	0 Missing and 3 partials ⚠️
.../github/eschizoid/telescope/effects/Validated.java	83.33%	1 Missing and 1 partial ⚠️
.../eschizoid/telescope/codegen/FromMapProcessor.java	0.00%	0 Missing and 1 partial ⚠️
...oid/telescope/codegen/MapperVerifierProcessor.java	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #222   +/-   ##
=========================================
  Coverage     79.59%   79.60%           
  Complexity     1841     1841           
=========================================
  Files            80       80           
  Lines          5783     5790    +7     
  Branches       1215     1209    -6     
=========================================
+ Hits           4603     4609    +6     
- Misses          660      662    +2     
+ Partials        520      519    -1     

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[Copilot]

Pull request overview

This PR raises the project’s Java compile baseline to Java 21 (while keeping the Gradle toolchain at 25) and reintroduces Java 21 language/library features that were previously removed for Java 17 compatibility.

Changes:

• Bump Gradle options.release across modules to 21, and bump annotation processors to @SupportedSourceVersion(RELEASE_21).
• Restore Java 21 language features (pattern-matching switch, record patterns) in core and examples.
• Adopt Sequenced Collections APIs (getFirst()) and restore ExecutorService try-with-resources usage in tests/docs.

Reviewed changes

Copilot reviewed 34 out of 34 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
spring-boot-starter/build.gradle.kts	Raise compile release to 21.
README.md	Update JVM badge to 21+.
quarkus/build.gradle.kts	Raise compile release to 21.
lombok/src/main/java/io/github/eschizoid/telescope/codegen/lombok/LombokFocusProcessor.java	Processor source version to RELEASE_21.
lombok/build.gradle.kts	Raise compile release to 21.
internal/build.gradle.kts	Raise compile release to 21.
examples/springboot/product-starter/build.gradle.kts	Raise compile release to 21.
examples/springboot/org-chart/build.gradle.kts	Raise compile release to 21.
examples/springboot/order-jpa/src/main/java/io/github/eschizoid/telescope/demo/spring/api/ValidatedOrderController.java	Switch-based sealed dispatch in controller.
examples/springboot/order-jpa/build.gradle.kts	Raise compile release to 21 (but header comment now inconsistent).
examples/springboot/invoicing/src/test/java/io/github/eschizoid/telescope/demo/invoicing/InvoiceBridgeFlowTest.java	Use List.getFirst() in assertions.
examples/springboot/invoicing/build.gradle.kts	Raise compile release to 21.
examples/mapstruct-vs-telescope/src/test/java/io/github/eschizoid/telescope/example/mapstruct/MapStructVsTelescopeTest.java	Use getFirst() in tests.
examples/mapstruct-vs-telescope/build.gradle.kts	Raise compile release to 21.
examples/library/src/main/java/io/github/eschizoid/telescope/examples/MultiEditDemo.java	Use getFirst() in demo output paths.
examples/library/src/main/java/io/github/eschizoid/telescope/examples/DeepMappingDemo.java	Use getFirst() in demo output paths.
examples/library/build.gradle.kts	Raise compile release to 21.
core/src/test/java/io/github/eschizoid/telescope/introspection/MapperLoggingTest.java	Use getFirst() for sequenced collections.
core/src/test/java/io/github/eschizoid/telescope/BoundedAsyncTest.java	Restore try-with-resources on ExecutorService.
core/src/main/java/io/github/eschizoid/telescope/Telescope.java	Restore try-with-resources example; make BridgeTelescope private again.
core/src/main/java/io/github/eschizoid/telescope/runtime/instances/ValidatedK.java	Use record patterns for Invalid + List.getFirst() support via imports.
core/src/main/java/io/github/eschizoid/telescope/runtime/instances/EitherK.java	Restore sealed switch dispatch in map2.
core/src/main/java/io/github/eschizoid/telescope/effects/Validated.java	Restore sealed switch + record patterns in combine logic.
core/src/main/java/io/github/eschizoid/telescope/effects/Either.java	Restore sealed switch dispatch in fold.
core/src/main/java/io/github/eschizoid/telescope/DeepMap.java	Restore record patterns and sealed switch for mapping dispatch.
core/build.gradle.kts	Raise compile release to 21.
codegen/src/main/java/io/github/eschizoid/telescope/codegen/MapperVerifierProcessor.java	Use getFirst() in argument selection.
codegen/src/main/java/io/github/eschizoid/telescope/codegen/FromMapProcessor.java	Processor source version to RELEASE_21; getFirst() for single arg access.
codegen/src/main/java/io/github/eschizoid/telescope/codegen/FocusProcessor.java	Processor source version to RELEASE_21; getFirst() for single element access.
codegen/src/main/java/io/github/eschizoid/telescope/codegen/BridgeProcessor.java	Processor source version to RELEASE_21; getFirst() for container/type arg access.
codegen/src/main/java/io/github/eschizoid/telescope/codegen/BeanFocusProcessor.java	Processor source version to RELEASE_21.
codegen/src/main/java/io/github/eschizoid/telescope/codegen/AbstractTelescopeProcessor.java	Use getFirst() for single property handling.
codegen/build.gradle.kts	Raise compile release to 21.
benchmarks/build.gradle.kts	Raise compile release to 21.

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[Copilot]

Pull request overview

Copilot reviewed 36 out of 36 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 36 out of 36 changed files in this pull request and generated no new comments.